This invention relates generally to panels applied to framing in residential and other types of light construction. More particularly, the invention relates to panels able to resist lateral forces imposed by high wind and earthquake loads in regions where they are required by building codes. Such panels, commonly known as shear walls or diaphragms, must demonstrate shear resistance as shown in recognized tests, such as ASTM E72-05 (effective 2005).
The sheathing panels are measured to determine the load which the panel can resist within the allowed deflection without failure. The shear rating is generally based on testing of three identical 8×8 ft (2.44×2.44 m) assemblies, i.e., panels fastened to framing. One edge is fixed in place while a lateral force is applied to a free end of the assembly until the load is no longer carried and the assembly fails.
The measured shear strength will vary, depending upon the thickness of the panel and the size and spacing of the nails used in the assembly. For example, a typical assembly, e.g., a nominal ½ inch (12.7 mm) thick plywood fastened with 8d nails (see the nail description below) to nominal 2×4 inch (50.8×101.6 mm) wood studs spaced 16 inches (406.4 mm) apart (on centers), the nails being spaced 6 inches (152.4 mm) apart on the perimeter and 12 inches (304.8 mm) apart within the perimeter, would be expected to show a shear strength of 720 lbs/ft (1072 kg/m) before failure occurs. (Note the measured strength will vary as the nail size and spacing is changed, as the ASTM E72 test provides.) This ultimate strength will be reduced by a safety factor, e.g., a factor of three, to set the design shear strength for the panel.
U.S. Pat. No. 6,620,487 to Tonyan et al., incorporated herein by reference in its entirety, discloses a reinforced, lightweight, dimensionally stable structural cement panel (SCP) capable of resisting shear loads when fastened to framing equal to or exceeding shear loads provided by plywood or oriented strand board panels. The panels employ a core of a continuous phase resulting from the curing of an aqueous mixture of calcium sulfate alpha hemihydrate, hydraulic cement, an active pozzolan and lime, the continuous phase being reinforced with alkali-resistant glass fibers and containing ceramic microspheres, or a blend of ceramic and polymer microspheres, or being formed from an aqueous mixture having a weight ratio of water-to-reactive powder of 0.6/1 to 0.7/1 or a combination thereof. At least one outer surface of the panels may include a cured continuous phase reinforced with glass fibers and containing sufficient polymer spheres to improve nailability or made with a water-to-reactive powders ratio to provide an effect similar to polymer spheres, or a combination thereof.
U.S. Pat. No. 6,241,815 to Bonen, incorporated herein by reference in its entirety, also discloses formulations useful for SCP panels.
U.S. Pat. No. 7,445,738 to Dubey, incorporated herein by reference, discloses a multi-layer process for producing structural cementitious panels (SCP's or SCP panels), and SCP's produced by such a process. After one of an initial deposition of loosely distributed, chopped fibers or a layer of slurry upon a moving web, fibers are deposited upon the slurry layer. An embedment device mixes the recently deposited fibers into the slurry, after which additional layers of slurry, and then chopped fibers are added, followed by more embedment. The process is repeated for each layer of the board, as desired.
US Patent Application Publication No. 2009/0011207 A1 to Dubey, incorporated herein by reference, discloses a fast setting lightweight cementitious composition for construction of panels or boards. The cementitious composition includes 35-60 wt. % cementitious reactive powder (also termed Portland cement-based binder), 2-10 wt. % expanded and chemically coated perlite filler, 20-40 wt. % water, entrained air, for example 10-50 vol. %, on a wet basis, entrained air, and optional additives such as water reducing agents, chemical set-accelerators, and chemical set-retarders. The lightweight cementitious compositions may also optionally contain 0-25 wt. % secondary fillers, for example 10-25 wt. % secondary fillers. Typical filler include one or more of expanded clay, shale aggregate, and pumice. The cementitious reactive powder used is typically composed of either pure Portland cement or a mixture of Portland cement and a suitable pozzolanic material such as fly ash or blast furnace slag. The cementitious reactive powder may also optionally contain one or more of gypsum (land plaster) and high alumina cement (HAC) added in small dosages to influence setting and hydration characteristics of the binder.
U.S. Pat. No. 4,304,704 to Billings discloses thermal insulating material containing silicone treated perlite and an admixture with gypsum and cement.
U.S. Pat. No. 5,601,919 to Symons discloses a building component having a core formed from one or more sheets of natural fiber impregnated with a liquid composition including a thermoplastic resin and a catalyst for setting the resin and an encapsulating layer encapsulating the core which can contains a hydraulic binder and water wherein the binder is selected from Portland cement or calcium sulphate hemihydrate at 15-65 parts by weight and a filler which can be expanded vermiculite or perlite. The expanded perlite is of 0.05 mm to 3 mm particle size which is treated with silicone to make it hydrophobic.
There remains a need for improved panels which can meet the shear rating required in certain locations and which exceed the capability of the currently-used wood-based panels as well as current gypsum-cement based structural cement panels by providing a non-combustible panel with the same shear strength at lower panel weight which also has improved water durability and thermal resistance.